Known in the art is U.S. Pat. No. 5,377,731 (Wildey) which shows a saw blade of a type which is used in a tree felling head. The saw blade has a disc provided with tooth holders about its periphery which support cutting teeth asymmetrically above an inner plate of the disc. As shown in FIG. 1, the tooth holders are in the form of protrusions radially projecting from the rim of the disc. Each tooth holder has a transverse central mounting bore. The mounting bore has a larger diameter on one side to receive the shank of a tooth, and a smaller diameter on the other side to receive the shank of a bolt screwed in the shank of the tooth to hold it in place on the tooth holder. One problem with this tooth retaining system is that the tooth holders must be sufficiently spaced from one another to leave enough space for passage of the bit used to drill the mounting bores, thereby limiting the number of possible teeth and tooth holders around the saw blade (e.g. to 18 teeth) and forcing them to be undesirably remote from one another, which reduce the cutting efficiency of the saw blade. Also, the impact on the outer edge of the teeth produces a shearing force on the tooth retaining system, i.e. the shanks of the teeth and the bolts, causing premature wear due to the configuration of the teeth and of the tooth holders. The tooth holders may be separate from the disc, in which case they form a part of the rim of the disc and are fastened to it using bolts extending across superimposed portions of the tooth holders and the disc. Such a mounting arrangement is expensive and presents certain risks for the blade such as holders becoming loose and cracks at the periphery of the blade originating from the mounting holes, in addition to safety risks.